Enter the time you’d like to wake up in our tool below and, based on 90-minute sleep cycles, we can tell you the best times to go to bed to wake up feeling fresh.

So for example, you still wake up at 4:30 in the morning ... I recommend that you go to bed earlier, 'cause what are you doing at night, most of the time? Most of the time at night, you're ...

REM stages and one REM stage. Ideally, you repeatedly cycle through each stage. Learn how long each stage lasts.